WASHINGTON - Biden administration officials announced Tuesday a new strategy to split monkeypox vaccine doses in hopes of vaccinating up to five times as many people against the virus.

The plan, unveiled days after the federal government declared monkeypox a public health emergency amid criticism over the administration's response to the rapidly unfolding crisis, would allow public health officials to stretch their limited supply of monkeypox vaccine doses by changing how those shots are administered. Rather than inject doses of Jynneos subcutaneously, a traditional way of delivering vaccines into the fatty tissue under the skin, the doses would instead be injected under the top layer of the skin. This approach, known as an intradermal injection, uses a thinner needle and less vaccine but leads to a small bubble forming on the surface of the skin that can scar.

Health and Human Services Secretary Xavier Becerra issued a declaration Tuesday that would allow for emergency use of the existing monkeypox vaccine, a move swiftly followed by the Food and Drug Administration granting emergency authorization for officials to inject the shots differently for adults. The move also allows minors to receive the monkeypox vaccine, which is only approved by the FDA for adults, through the traditional approach if they are deemed at high risk of infection.

The change in injection method would maximize the immune reaction generated by the vaccine and allow U.S. officials to only administer one-fifth of the original dose, officials said, stressing that the approach would not compromise safety or efficacy.

"It's safe, it's effective, and it will significantly scale the volume of vaccine doses available for communities across the country," Robert Fenton Jr., coordinator of the nation's monkeypox response, told reporters Tuesday.

FDA Commissioner Robert Califf has compared the new method, which he first described publicly last week, to tests for tuberculosis and other injections routinely performed by health-care workers.

But the change in vaccine dosing would be a large-scale, real-time experiment as officials race to stave off a monkeypox outbreak that has infected nearly 9,500 people in the United States. The announcement has drawn support as well as skepticism among public health experts eager to combat the virus, with some questioning its practicality and effectiveness.

If successful, the new vaccine plan would allow the Biden administration to transform about 441,000 existing doses of Jynneos - the only FDA-approved vaccine for monkeypox - into more than 2 million potential shots, officials said Tuesday. Although U.S. officials received more than 1.1 million doses of Jynneos this year, demand has rapidly outpaced supply and more doses are not expected for weeks.

The Biden administration has faced sustained criticism from patients, local public health officials and some lawmakers for not ordering more doses of the monkeypox vaccine earlier in the response. Federal officials consider at least 1.6 million gay and bisexual men at highest risk for the virus and are urging them to get the shots.

The change is not without risk. People who receive the pared-down version of the Jynneos vaccine, which is intended as a two-dose regimen, may end up needing additional shots if the new vaccine strategy leads to an insufficient level of protection against the virus. Local officials may also struggle to administer the new strategy, which could require additional training and supplies like new needles to safely deliver the shots.

"Actually being able to get the shots in the arms as fast as possible is our primary issue," said Kody Kinsley, North Carolina's top public health official.

He noted that many vaccine administrators familiar with injecting shots into muscles would need to be retrained and that public health officials are struggling to maintain the necessary staffing to meet demand. Some health authorities are recruiting school nurses on summer break to help administer the shots. In Charlotte, the epicenter of the state's outbreak, officials are able to give 300 shots a day but have a waitlist of 2,200 that is growing by several hundred a day, Kinsley said.

The Centers for Disease Control and Prevention plans to release guidance for health-care workers on how to administer the new vaccine strategy as part of an outreach campaign.

David Harvey, executive director of the National Coalition of STD Directors, said sexual health clinics are severely underfunded and not well-positioned to administer more doses under the new plan. He also questioned whether the new approach would work.

"We have grave concerns about the limited amount of research that has been done on this dose and administration method, and we fear it will give people a false sense of confidence that they are protected," Harvey said in a written statement. "This approach raises red flag after red flag, and appears to be rushed ahead without data on efficacy, safety, or alternative dosing strategies."

Michael Osterholm, director of the Center for Infectious Disease Research and Policy at the University of Minnesota, said he had concerns about the immune protection provided by the strategy, particularly for people with health conditions like HIV. "We don't yet have the data to know how effectively an intradermal-administered vaccination will protect immunocompromised persons," he said.

Administration officials worked through the weekend on the logistics of the new strategy, drawing on prior studies into splitting vaccine doses, which is often referred to as "dose-sparing." The FDA in its Tuesday announcement cited a 2015 study of the two-dose vaccine that found similar immune responses after intradermal shots, although with more redness and itchiness at the injection site.

Other outside experts signaled their support for the idea. Daniel McQuillen, president of the Infectious Diseases Society of America, said in a statement that his organization agrees with the strategy.

The plan is "supported by compelling evidence of an equally strong immune response compared to the current strategy and could be an effective way to achieve the important goal of vaccinating more people," McQuillen wrote.

But he noted that changing the way the shots would be administered could create new challenges, such as the greater risk of a skin reaction at the injection site. "For this strategy to succeed, strong public education about the way to correctly administer the vaccine intradermally and collection of data on its impacts will be essential."

Scott Gottlieb, who served as commissioner of the FDA during the Trump administration, said officials were drawing on existing research into vaccines used for smallpox, a related virus.

"There's a lot of data that FDA has looked at . . . [on] how we would extend doses of the smallpox vaccine. What they learned from those studies is transferrable to this vaccine for monkeypox," Gottlieb said on CBS's "Face the Nation" on Sunday.

But Osterholm, who served as state epidemiologist in Minnesota, said his team regularly dealt with problems where seasoned public health workers struggled with administering the injections needed for tuberculosis testing.

"This is a well-recognized issue where intradermal injections can be tough to do, without adequate training," he said.